This reference design significantly extends the hold-up time beyond 10 ms without bulky output capacitor bank. A 60-V high voltage energy storage capacitor is utilized on the input side. It instantaneously connects to a flyback converter when a line interruption is detected: charges up the input capacitor and extends the hold-up time. The active switch circuitry is fast-acting and current-limiting. By removing the bulky output capacitor bank: it further reduces the total solution size. It is a compact solution for isolated power supply where a long hold-up time is required.